Strategy and current status of combating eutrophication in two Berlin lakes for safeguarding drinking water resources

After reduction of the external phosphorus load by phosphorus elimination plants, Lake Tegel and Schlachtensee in Berlin underwent a significant trophic improvement. The phosphorus elimination plants work by precipitation/coagulation/flocculation – sedimentation – post precipitation – filtration. The external load was reduced by one to two orders of magnitude down to 10–20 μg P L −1 .The inlake phosphorus concentration followed. The development of algae and cyanobacteria was reduced substantially below a threshold value of about 50 μg P L −1 , clearly due to phosphorus limitation. In Lake Tegel, the external load reduction of the main inflow was counteracted partially by the external load of the second main inflow by the River Havel and the internal load. This has to be managed further in future.